1. Field of the Invention
This invention relates generally to telecommunication access systems and, in particular, to switched video telecommunication access systems.
2. Description of the Related Art
In many existing telecommunication access systems, such as cable systems and satellite systems, video programming on a predefined number of channels is broadcast to all subscribers units in the system. In other words, each subscriber unit receives the video programming of all the channels in the system. For each subscriber unit, the number of video programs that may be displayed at any point in time is limited by the total number of display devices (in addition to the number of display devices having the picture-in-picture feature) within the subscriber unit that are connected to the system. More specifically, for each subscriber unit, the number of video programs displayed at any point in time is limited by the number of display devices activated for displaying video programming. As the number of display devices within a subscriber unit, and more specifically the number of activated display devices within a subscriber unit, is generally much smaller than the number of channels in the system, video programs on a number of channels are not displayed at any given time. The broadcasting of undisplayed video programs occupies valuable bandwidth which is wasted.
Another disadvantage of broadcasting programs to all subscribers is that of potential unauthorized viewing of pay-per-view or premium channel programs. This problem is largely overcome by sending programs on pay-per-view and premium channels in scrambled mode and providing only authorized subscribers with means for unscrambling the programs. However, the problem is far from entirely eliminated as these programs may be descrambled by using unauthorized descrambling devices.
One prior art method of reducing theft is to use a switched rather than a broadcast system to transmit video programs to the subscriber units. In a switched system, video programs are sent to a subscriber unit in response to a request received from the subscriber unit. Although prior art switched systems generally provide greater protection against unauthorized viewing of programs, they do not address other issues that are recognized and addressed by the present invention.
One of the issues recognized and addressed by the present invention is the minimization of bandwidth used when transmitting a video program on a particular channel to multiple display devices associated with one gateway device. Thus, when a video program on a particular channel is requested for display on more than one display device associated with one gateway device, only one stream of video data representing the video program on the particular channel is transmitted to the one gateway device. Sending only one stream of video data representing a video program on a particular channel, rather than sending multiple streams of video data representing the video program on the same channel, reduces the amount of bandwidth used for transmitting to a gateway device a video program on a particular channel requested for display on multiple display devices associated with the gateway device. The gateway device distributes the video program to one or more display units within the gateway device on which the video program on the particular channel is requested to be displayed.
Similarly, only one stream of video data representing video programming on a particular channel is sent from the broadband digital terminal (BDT) to an optical network unit (ONU) even when more than one gateway device associated with a particular ONU request the video data on the particular channel. Therefore, only one stream of video data representing video programming on a particular channel is transmitted from the BDT to any one ONU. The ONU then sends the video data to each gateway device associated with the ONU which requests the video program on the particular channel. For each gateway device requesting the video program on the particular channel, the ONU sends only one stream of video data representing the video programming on the particular channel. Sending of one rather than multiple streams of video data representing the video programming on the particular channel saves considerable bandwidth that would otherwise be wasted on sending multiple copies of the video program on the particular channel from the BDT to the one or more ONUs and from the one or more ONUs to the one or more gateway devices.
In a presently preferred embodiment of the present invention, the stream of video data is transmitted to the gateway device in ATM cells. Video data representing the video programming on a particular channel is identified with only one Virtual Path Identifier (VPI) and one Virtual Channel Identifier (VCI) throughout the system. Therefore, only one VPI and one VCI is used to identify the video data representing the video programming on a particular channel as the video data is transmitted from the BDT to any ONU in the system. Similarly, the same VPI and VCI is used to identify the video data representing the video programming on the particular channel as the video data is transmitted between any ONU and any gateway device associated with the ONU. This allows sending only one stream of video data representing the video programming on a particular channel from the BDT to any one ONU and from any one ONU to any one gateway device associated with the ONU. Use of only one VPI and one VCI, rather than a multiple number of VPIs and VCIs, reduces the amount of bandwidth used for transmitting video data from the BDT to the ONUs and from the ONUs to the gateway devices. The ONU multicasts the video program to all the gateway devices associated with the ONU requesting the video program. Similarly, the gateway device multicasts the video program to all the display devices associated with the gateway device on which the video program on the particular channel is to be displayed.
In a presently preferred embodiment of the invention, the switched telecommunication access system comprises: a switched multicasting station for transmitting video data in response to receiving a video data request signal; and a plurality of gateway devices coupled to the switched multicasting station, the gateway devices sending video data request signals to the switched multicasting station and receiving video data from the switched multicasting station, at least one gateway device of the plurality of gateway devices comprising: a controller for sending a video data request signal to the switched multicasting station and for routing video data received from the switched multicasting station in response to the video data request signal; and a plurality of video decoders coupled to the controller for decoding the video data received from the switched multicasting station; wherein one stream of video data representing a video program on a particular channel is sent from the switched multicasting station to one gateway device of the plurality of gateway devices even when the video program on the particular channel is requested for display on more than one display device coupled to the one gateway device.
In another presently preferred embodiment of the invention, the switched telecommunication access system comprises: a switched multicasting station for transmitting video data in response to receiving a video data request signal; and a plurality of gateway devices coupled to the switched multicasting station, the gateway devices sending video data request signals to the switched multicasting station and receiving video data from the switched multicasting station, at least one gateway device of the plurality of gateway devices comprising: a plurality of video decoders for decoding video data received from the switched multicasting station; and a controller for sending a video data request signal to the switched multicasting station and for routing video data received from the switched multicasting station in response to the video data request signal, the controller comprising: a plurality of selectors, each selector of the plurality of selectors receives a plurality of video data streams and in response to a control signal from the controller selects one video data stream of the plurality of video data streams for transmission to one of the plurality of video decoders.
The present invention is explained in more detail below with reference to the drawings.